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What Happens If You Use The Wrong Size AC Filter?

23 May 2023

Abbie Wade

Your home's air conditioning filter is a surprisingly important part of your overall HVAC system. While this low-cost part might seem minor, a dirty or incorrectly-sized filter can ruin your system's efficiency or even cause serious damage to more expensive components. Surprisingly, this part that may only cost a few dollars can often be responsible for many unnecessary maintenance and service calls.

The best way to ensure your system runs as reliably and efficiently as possible is to change your filter regularly with replacements of the proper size and design. If you haven't thought much about AC filter changes in the past, this guide will explain how filter sizes work, why using the correct filter size is essential, and what you can do to select the appropriate filter for your system.

The Basics of Filter Sizes

Air conditioning filters come in a wide array of sizes. Filter sizes include: width, height, and depth (or thickness). When choosing a filter for your air conditioner, you must choose the exact size necessary for your particular air handler. Although other sizes may physically fit in your air handler box, an incorrect size can seriously affect your system.

Note that the thickness of your filter will also affect your replacement intervals. Thicker filters have more overall surface area, which allows them to last longer before requiring a change. A 5" filter can last as long as a full year between changes, while a 1" filter may require changes every month or even more frequently. Knowing your AC filter thickness is essential to know how often you should change it.

How Incorrect Filter Sizes Affect Your System

The primary role of your filter is to protect your air conditioning system's evaporator coil from dust and debris. An excessive amount of dust will act as a layer of insulation, preventing the evaporator from absorbing heat. However, the filter must also allow enough airflow to prevent the evaporator coil from becoming too cold and freezing.

Using a filter that's too small can allow air to flow around the filter, permitting dust, hair, and other contaminants onto the evaporator coils. On the other hand, filters that are too large may bend or deform, restricting airflow or causing the filter to tear. Your system also expects a certain amount of pressure to drop across the filter, so using the correct filter thickness is essential to maintain airflow.

Choosing the Best Filter for Your System

While you can't often choose your filter size, you can choose your filter efficiency. The MERV rating tells you the smallest contaminants your filter will catch, and filters of every size are available with a range of MERV ratings. While any MERV rating will protect your air conditioning system, higher MERV ratings can also help improve your home's indoor air quality.

Choosing an appropriately-sized filter with a higher MERV rating can ensure your evaporator coil remains clean while filtering out pet dander, allergens, and other contaminants that may affect indoor air quality. Reach out to a local AC service to learn more.

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